Performance assessment and adaptation of an acoustic communication link

ABSTRACT

Systems and methods for adapting the performance of an acoustic communication link with an implantable medical device (IMD) are disclosed. An illustrative method includes initiating an acoustic link with the IMD, measuring an initial performance of the acoustic link, determining whether the initial performance of the acoustic link is adequate, adjusting an operating parameter related to the acoustic link in the event the initial performance of the acoustic link is inadequate, measuring a performance of the acoustic link in response to the adjusted operating parameter, and setting the operating parameter to a prior setting if the measured performance of the acoustic link does not improve in response to the adjusted operating parameter.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 to U.S.Provisional Application No. 61/088,891, filed on Aug. 14, 2008, entitled“Performance Assessment And Adaptation of an Acoustic CommunicationLink,” which is incorporated herein by reference in its entirety for allpurposes.

TECHNICAL FIELD

The present invention relates generally to implantable medical devices.More particularly, the present invention relates to systems and methodsfor adapting an acoustic communication link with an implantable medicaldevice.

BACKGROUND

Implantable medical devices (IMDs) such as pacemakers and implantablecardioverter defibrillators are utilized in monitoring and regulatingvarious conditions within the body. An implantable cardioverterdefibrillator, for example, may be utilized in cardiac rhythm managementapplications to monitor the rate and rhythm of the heart and fordelivering various therapies such as cardiac pacing, cardiacdefibrillation, and/or cardiac therapy. In some cases, the IMD can beconfigured to sense various physiological parameters occurring withinthe body to determine the occurrence of any abnormalities in theoperation of the patient's heart. Based on these sensed parameters, theIMD may then deliver an appropriate treatment to the patient.

Communication with IMDs is sometimes accomplished via a wirelesstelemetry link between an external device and the IMD, or between theIMD and another device located within the body. In some cases,ultrasonic transducers can be used to establish an acoustic link withthe IMD, allowing data, operational status, and other information to bewirelessly transmitted through the body via an acoustic signal.Establishing and maintaining an acoustic link between the IMD and thecommunicating device is often difficult, however, based on the acousticpath between the IMD and the communicating device. In some cases, forexample, the acoustic link can be compromised by the presence of bodyorgans, vessels, airways, and other anatomical structures within thebody. Factors that can affect the performance of the acoustic link caninclude the implant location of the IMD within the body, the orientationof the IMD within the body, the presence of physiological noise (e.g.,heart sounds, vibration, etc.) within the body, and the presence of bodytissue interfaces or other areas where there is an abrupt change inacoustic impedance that can cause reflections and absorption of theacoustic signal.

SUMMARY

The present invention relates to methods and systems for adapting anacoustic communication link with an implantable medical device. Anillustrative method of adapting the performance of an acousticcommunication link includes initiating an acoustic link with theimplantable medical device, measuring an initial performance of theacoustic link, determining whether the initial performance of theacoustic link is adequate, adjusting at least one operating parameterrelated to the acoustic link in the event the initial performance of theacoustic link is inadequate, measuring a performance of the acousticlink in response to the adjusted operating parameter, and setting theoperating parameter to a previous setting if the measured performance ofthe acoustic link does not improve in response to the adjusted operatingparameter.

A system in accordance with an exemplary embodiment includes animplantable medical device equipped with a physiological sensor and anacoustic transducer adapted to transmit and receive acoustic signals, acommunicating device in acoustic communication with the implantablemedical device via an acoustic link, and a processor adapted to adjustat least one operating parameter of the implantable medical deviceand/or the communicating device in response to a measured performanceparameter of the acoustic link. In some embodiments, the communicatingdevice comprises an external device having an acoustic transducer thattransmits and receives acoustic signals to and from the implantablemedical device. In other embodiments, the communicating device comprisesanother implanted device that transmits and receives acoustic signals toand from the implantable medical device. In one embodiment, theimplantable medical device comprises a remote device having a pressuresensor adapted to sense blood pressure within a body vessel.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. Accordingly, the drawings anddetailed description are to be regarded as illustrative in nature andnot restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an illustrative system employing a remoteimplantable medical device located within the body of a patient;

FIG. 2 is a block diagram of an illustrative embodiment of theimplantable medical device of FIG. 1;

FIG. 3 is a block diagram of an illustrative embodiment of the externaldevice of FIG. 1;

FIG. 4 is a flow chart showing an illustrative method of adapting anacoustic communication link with an implantable medical device;

FIG. 5 is a flow chart showing another illustrative method of adaptingan acoustic communication link with an implantable medical device; and

FIG. 6 is a flow chart showing an illustrative implementation of themethod of FIG. 4.

While the invention is amenable to various modifications and alternativeforms, specific embodiments have been shown by way of example in thedrawings and are described in detail below. The intention, however, isnot to limit the invention to the particular embodiments described. Onthe contrary, the invention is intended to cover all modifications,equivalents, and alternatives falling within the scope of the inventionas defined by the appended claims.

DETAILED DESCRIPTION

FIG. 1 is a schematic view of an illustrative system 10 employing aremote implantable medical device (IMD) located within the body of apatient. The system 10, illustratively a cardiac rhythm managementsystem for providing cardiac rhythm management to a patient, includes anexternal monitor 12 (e.g., an external wand or programmer), a pulsegenerator 14 implanted within the body at a location below the patient'sskin, and at least one remote IMD 16 implanted deeply within thepatient's body such as in one of the arteries or ventricles of thepatient's heart 18. The heart 18 includes a right atrium 20, a rightventricle 22, a left atrium 24, a left ventricle 26, and an aorta 28.The right ventricle 22 leads to the main pulmonary artery 30 and thebranches 32,34 of the main pulmonary artery 30. Typically, the pulsegenerator 14 will be implanted at a location adjacent to the location ofthe external monitor 12, which may lie adjacent to the exterior surfaceof the patient's skin.

In the illustrative system 10 depicted, the pulse generator 14 iscoupled to a lead 36 deployed in the patient's heart 18. The pulsegenerator 14 can be implanted subcutaneously within the body, typicallyat a location such as in the patient's chest or abdomen, although otherimplantation locations are possible. A proximal portion 38 of the lead36 can be coupled to or formed integrally with the pulse generator 14. Adistal portion 40 of the lead 36, in turn, can be implanted at a desiredlocation within the heart 18 such as the right ventricle 22, as shown.Although the illustrative system 10 depicts only a single lead 36inserted into the patient's heart 18, it should be understood, however,that the system 10 may include multiple leads so as to electricallystimulate other areas of the heart 18. In some embodiments, for example,the distal portion of a second lead (not shown) may be implanted in theright atrium 20. In addition, or in lieu, another lead may be implantedin the left side of the heart 18 (e.g., in the coronary veins) tostimulate the left side of the heart 18. Other types of leads such asepicardial leads may also be utilized in addition to, or in lieu of, thelead 36 depicted in FIG. 1.

During operation, the lead 36 is configured to convey electrical signalsbetween the heart 18 and the pulse generator 14. For example, in thoseembodiments where the pulse generator 14 is a pacemaker, the lead 36 canbe utilized to deliver electrical therapeutic stimulus for pacing theheart 18. In those embodiments where the pulse generator 14 is animplantable cardiac defibrillator, the lead 36 can be utilized todeliver electric shocks to the heart 18 in response to an event such asa ventricular fibrillation. In some embodiments, the pulse generator 14includes both pacing and defibrillation capabilities.

The remote IMD 16 can be configured to perform one or more designatedfunctions, including the sensing of one or more physiological parameterswithin the body. Example physiological parameters that can be measuredusing the remote IMD 16 can include, but are not limited to, bloodpressure, blood flow, temperature, and strain. Various electrical,chemical, magnetic, and/or sound properties may also be sensed withinthe body via the remote IMD 16. In one embodiment, the remote IMD 16 isadapted to deliver a desired therapy (e.g., a pacing and/ordefibrillation stimulus) to the patient's heart 18 or cardiovascularsystem.

In the embodiment of FIG. 1, the remote IMD 16 comprises a pressuresensor implanted at a location deep within the body such as in the mainpulmonary artery 30 or a branch 32,34 of the main pulmonary artery 30(e.g., in the right or left pulmonary artery). An exemplary pressuresensor suitable for use in sensing pulmonary arterial pressure isdescribed in U.S. Pat. No. 6,764,446, entitled “Implantable PressureSensors and Methods for Making and Using Them,” which is incorporatedherein by reference in its entirety for all purposes. In use, the remoteIMD 16 can be used to aid in the prediction of heart decompensation of aheart failure patient and/or to aid in optimizing pacing and/ordefibrillation therapy via the pulse generator 14 by taking pressuremeasurements within the body. In some embodiments, the remote IMD 16 canbe configured to sense, detect, measure, calculate, and/or derive otherassociated parameters such as flow rate, maximum and minimum pressure,peak-to-peak pressure, rms pressure, and/or pressure rate change. Forexample, in some embodiments, the pressure signal from the remote IMD 16can be used to detect changes in arterial blood pressure during acardiac cycle or across multiple cardiac cycles.

The remote IMD 16 may be implanted in other regions of the patient'svasculature, in other body lumens, or in other areas of the body, andmay comprise any type of chronically implanted device adapted to delivertherapy and/or monitor biological and chemical parameters, properties,and functions. The remote IMD 16 can be tasked, either alone or withother implanted or external devices, to provide various therapies withinthe body. In certain embodiments, for example, the remote IMD 16 maycomprise a glucose level sensor that can be used in conjunction with aninsulin pump for providing insulin treatment to the patient. Although asingle remote IMD 16 is depicted in FIG. 1, multiple such devices couldbe implanted at various locations within the body for sensingphysiologic parameters and/or providing therapy at multiple regionswithin the body.

An acoustic communication link may be established to permit wirelesscommunications between the remote IMD 16 and the external device 12,between the remote IMD 16 and the pulse generator 14, and/or between theremote IMD 16 and another communicating device located inside or outsideof the body. In the illustrative system 10 of FIG. 1, for example, theexternal device 12 includes an acoustic transducer 42 adapted totransmit an acoustic signal 44 into the body for establishing anacoustic link between the remote IMD 16 and the external device 12.

An acoustic transducer 46 coupled to the housing 48 of the remote IMD 16is configured to receive the acoustic signal 44 transmitted by theexternal device 12. An example acoustic transducer suitable for use withthe remote IMD 16 is described in U.S. Pat. No. 6,140,740, entitled“Piezoelectric Transducer,” which is expressly incorporated herein byreference in its entirety for all purposes. In some embodiments, thetransmission of the acoustic signal 44 to the remote IMD 16 can be usedto activate the IMD 16 from a low-power, sleep state to an active,energized state. In one embodiment, for example, the acoustic signal 44generated by the external device 12 can be used to wake up the remoteIMD 16 from an initial, low-power state to an active state to take oneor more sensor readings within the body and then transmit those readingsto the external device 12, to the pulse generator 14, and/or to anotherdevice located inside or outside of the body.

In some embodiments, the acoustic signal 44 can be used to provide powerto the remote IMD 16 and/or to recharge an energy storage device withinthe IMD 16 such as a rechargeable battery or power capacitor. In someembodiments, the acoustic signal 44 provides acoustical energy that canbe converted into electrical energy to provide therapy to the patient,if desired.

While the system 10 of FIG. 1 includes an external device 12 in acousticcommunication with a remote IMD 16, in other embodiments the system 10may employ other devices located inside or outside of the patient's bodythat acoustically communicate with the IMD 16. As further shown in FIG.1, for example, the pulse generator 14 can also include an acoustictransducer 50 adapted to transmit an acoustic signal 52 to the remoteIMD 16 to establish an acoustic link between the pulse generator 14 andthe remote IMD 16. In certain embodiments, the acoustic transducer 50 iscoupled to an interior portion of the can 54 that encloses the variouscomponents of the pulse generator 14. In other embodiments, the acoustictransducer 50 is located outside of the can 54, or is coupled to thepulse generator 14 through a feedthrough provided on the can 54.

Although the system 10 depicted in FIG. 1 shows an acoustic link betweenthe external device 12 and the remote IMD 16, and further between theIMD 16 and the pulse generator 14, in other embodiments an acoustic linkcan be established between the remote IMD 16 and another deviceimplanted within the body. In some embodiments, for example, an acousticcommunication link can be established between a primary IMD 16 and oneor more secondary IMDs 16 implanted within the body.

While the illustrative system 10 utilizes acoustic transducers towirelessly transfer data, control mode/function, operational parameters,and other information to and from the remote IMD 16, other modes ofwireless communication are also possible. Examples of other wirelessmodes of communication can include, but are not limited to, radiofrequency (RF), inductive, magnetic, or optical. In certain embodiments,several different modes of wireless communication can be utilized towirelessly transmit information through the body. In one suchembodiment, for example, an acoustic communication link is used toestablish wireless communications between the remote IMD 16 and theexternal device 12, and an RF or inductive communication link is used toestablish wireless communications between the pulse generator 14 and theexternal device 12. Other combinations of wireless communication modesare also possible.

FIG. 2 is a block diagram of an illustrative embodiment of the remoteIMD 16 of FIG. 1. As shown in FIG. 2, the remote IMD 16 includes anenergy storage device 56, a physiological sensor 58, an acoustic switch60 (including the acoustic transducer 46, a signal detector 62, and anactivation/deactivation switch component 64), power control circuitry66, and a controller 68. The energy storage device 56 may benon-rechargeable or rechargeable, and operates to supply power to thephysiological sensor 58, the acoustic switch 60, the power controlcircuitry 66, and the controller 68. The power control circuitry 66 isoperatively connected to the acoustic switch 60, and is used to regulatethe supply of power from the energy storage device 56 to thephysiological sensor 58 and the controller 68.

The physiological sensor 58 performs functions related to themeasurement of one or more physiological parameters within the body. Incertain embodiments, for example, the physiological sensor 58 comprisesa pressure sensor adapted to measure blood pressure in a body vessel. Inone such embodiment, the remote IMD 16 is implanted in a pulmonaryartery of the patient, and the physiological sensor 58 is adapted tosense arterial blood pressure. An example remote IMD 16 suitable forsensing blood pressure within an artery is described, for example, inU.S. Provisional Patent Application No. 61/060,877, entitled“Implantable Pressure Sensor with Automatic Measurement and StorageCapabilities,” which is expressly incorporated herein by reference inits entirety for all purposes. In other embodiments, the physiologicalsensor 58 is adapted to generate a signal related to other sensedphysiological parameters including, but not limited to, temperature,electrical impedance, position, strain, pH, blood flow, radiation level,and glucose level. In some embodiments, the remote IMD 16 may alsoinclude a therapy delivery module 70 that performs one or moretherapeutic functions (e.g., cardiac pacing, drug delivery) within thebody in addition to, or in lieu of, the one or more sensing functionsprovided by the physiological sensor 58.

The acoustic transducer 46 for the remote IMD 16 may include one or morepiezoelectric transducer elements configured to transmit and receiveacoustic signals. In a reception mode of operation, the acoustictransducer 46 is configured to receive the acoustic signal 44,52transmitted from the external device and/or the pulse generator 14,which is fed to the controller 68 when the remote IMD 16 is in theactive state. The acoustic transducer 46, or another acoustic transducercoupled to the remote IMD 16, is configured to transmit an outwardacoustic signal 71 to the external device 12 and/or the pulse generator14. The transmitted acoustic signal 71 can include sensor data obtainedfrom the physiological sensor 58, information relating to the status oroperation of the remote IMD 16 (e.g., power status, communication modestatus, error correction information, etc.), as well as otherinformation relating to the operation of the remote IMD 16.

The signal detector 62 is configured to generate an activation triggersignal to activate the remote IMD 16 via the activation/deactivationswitch component 64. The activation trigger signal is generated by thesignal detector 62 when the electrical signal generated by the acoustictransducer 46 exceeds a specific voltage threshold. Theactivation/deactivation switch component 64 is the component throughwhich current is delivered from the energy storage device 56 to thecontroller 68 when actuated.

In response to the generation of the activation trigger signal by thesignal detector 62, the switch component 64 is actuated to allow currentto flow to the controller 68, thereby placing the remote IMD 16 in theactive state. The switch component 64 can also be actuated to preventcurrent from flowing to the controller 68, thereby placing the remoteIMD 16 in the standby state. Further details regarding the generalconstruction and function of acoustic switches are disclosed in U.S.Pat. No. 6,628,989, entitled “Acoustic Switch And Apparatus And MethodsFor Using Acoustic Switches Within The Body,” which is expresslyincorporated herein by reference in its entirety for all purposes. Inother embodiments, the external device 12 or the pulse generator 14operates to generate a field (i.e., a wake-up field) that can bedetected by a sensing module in the remote IMD 16 for the purpose ofcausing the remote IMD 16 to wake from the sleep state. For example, theremote IMD 16 can include an antenna or inductive coil that receives anRF or inductive signal from the external device 12 or pulse generator 14to wirelessly activate or deactivate the remote IMD 16 within the body.

The controller 68 includes a processor 72 such as a microprocessor ormicrocontroller coupled to a memory device 74 that includes operatinginstructions and/or software for the remote IMD 16. The controller 70also includes an oscillator or other timing circuitry 76 which directsthe timing of activities performed by the remote IMD 16 once awoken fromits low-power or sleep state. For example, the timing circuitry 76 canbe used for timing the physiologic measurements taken by thephysiological sensor 58, and to generate timing markers to be associatedwith those measurements. The controller 68, including the processor 72,can be configured as a digital signal processor (DSP), a fieldprogrammable gate array (FPGA), an application specific integratedcircuit (ASIC)-compatible device, and/or any other hardware componentsor software modules for processing, analyzing, storing data, andcontrolling the operation of the remote IMD 16.

The processor 72 can be configured to analyze, interpret, and/or processthe received acoustic signals 44,52 as well as the signals received bythe physiological sensor 58. As discussed further herein with respect toFIGS. 4-6, the processor 72 is configured to run an adaptation algorithmor routine 78 that analyzes the performance of the acoustic link betweenthe remote IMD 16 and the external device 12 and/or pulse generator 14,and responsive to such feedback, adjusts one or more operatingparameters of the remote IMD 16 to ensure that the acoustic link isadequately maintained. A similar controller may be provided on the pulsegenerator 14 to permit the pulse generator 14 to measure an acousticlink established between the remote IMD 16 and the pulse generator, andresponsive to such feedback, adjust one or more operating parameters ofthe pulse generator 14, if desired.

FIG. 3 is a block diagram of an illustrative embodiment of the externaldevice 12 of FIG. 1. As shown in FIG. 3, the external device 16 includesan acoustic transducer 42, an on-board sensor 80, a controller 82, auser feedback device 84, and an energy storage device 86. In someembodiments, the external device 12 is a handheld device. In otherembodiments, the external device 12 is attached to a portion of thepatient's body such as the patient's arm, neck, chest, thigh, or knee.The external device 12 can use any type of attachment mechanism, such asa strap, a patch, a belt, or any other means for coupling the device 12to the patient's body.

The sensor 80 may comprise a biosensor that generates a signal inresponse to a sensed physiological parameter. In one embodiment, forexample, the sensor 80 comprises a barometric pressure sensor configuredto measure barometric pressure for use in calibrating a pressure signalreceived from the remote IMD 16. The external device 12 may include oneor more additional sensors such as an ECG electrode sensor, a systemicblood pressure sensor, a posture sensor, a global positioning system(GPS) sensor, an activity sensor, a temperature sensor, a timer, and/oran oximeter.

The acoustic transducer 42 for the external device 12 is configured toboth transmit and receive acoustic signals to and from the pulsegenerator 14 and remote IMD 16. In other embodiments, the externaldevice 12 includes at least one transducer configured for receivingacoustic signals and at least one transducer for transmitting acousticsignals. The acoustic transducer 42 generates an electrical signalproportional to the magnitude of acoustic energy received by thetransducer 42, which is then conveyed to the controller 82. In similarfashion, the acoustic transducer 42 generates an acoustic signalproportional to the magnitude of the electrical energy generated by thecontroller 82.

The controller 82 includes circuitry for activating or controlling thesensor 80 and for receiving signals from the sensor 80. In someembodiments, the controller 82 may include an oscillator or other timingcircuitry 88 for use in modulating the acoustic signal transmitted tothe remote IMD 16 and/or the pulse generator 14 via the acoustictransducer 42. The controller 82 can also include signal detectioncircuitry 92 for detecting acoustic signals received from the remote IMD16 and/or the pulse generator 14 via the acoustic transducer 42.

The controller 82 includes a processor 94 for analyzing, interpreting,and/or processing the received acoustic signals, and a memory 96 forstoring the processed information and/or commands for use internally. Incertain embodiments, for example, the processor 94 can be used toanalyze the strength and quality of the acoustic signal received fromthe remote IMD 16 and/or the pulse generator 14. The controller 82,including the processor 94, can be configured as a digital signalprocessor (DSP), a field programmable gate array (FPGA), an applicationspecific integrated circuit (ASIC)-compatible device, and/or any otherhardware components or software modules for processing, analyzing,storing data, and controlling the operation of the external device 12.During operation, and as discussed further herein, the processor 94 canbe configured to run an algorithm or routine 98 that analyzes theperformance of the acoustic link between the external device 12 and theremote IMD 16 and/or the pulse generator 14, and responsive to suchfeedback, adjusts one or more operating parameters of the externaldevice 12 to ensure that the acoustic link is adequately maintained.

The user feedback device 84 can include a screen or display panel forcommunicating information to a clinician and/or to the patient. Forexample, the screen or display panel can display information indicativeof the strength and/or quality of the acoustic signal received from theremote IMD 16 and/or from the pulse generator 14. The user feedbackdevice 84 can also be configured to display information relating tovarious operating parameters and status information of the externaldevice 12, the remote IMD 16, and/or the pulse generator 14. Forexample, the user feedback device 84 can display information regardingthe transmission power or intensity of the acoustic signal 44transmitted to the remote IMD 16, the frequency of the transmittedacoustic signal 44, and the modulation format of the transmittedacoustic signal 44 (e.g., pulse code modulation (PCM), frequency shiftkeying (FSK), frequency modulation (FM), or amplitude modulation (AM)).The user feedback device 84 can also display other information regardingthe acoustic signal 44, including the occurrence of any communicationerrors that may have occurred.

The user feedback device 84 can also display information regarding theoperation of the remote IMD 16 and/or the pulse generator 14, includingthe transmission power or intensity of the acoustic signal 71transmitted by the acoustic transducer 46 for the remote IMD 16, thecarrier frequency of the acoustic signal 71 transmitted by the acoustictransducer 46, the bit/word timing and word resolution of the acousticsignal 71 transmitted by the acoustic transducer 46, and the samplingrate or word size of the acoustic signal 71 transmitted by the acoustictransducer 46. In certain embodiments, the user feedback device 84 canalso be used to display other information such as any physiologicalparameters sensed by the remote IMD 16, the power status of the remoteIMD 16, and the operating status of the pulse generator 14.

In some embodiments, the external device 12 can include an interface 100for connecting the device 12 to the Internet, an intranet connection, toa cell phone, and/or to other wired or wireless means for downloading oruploading information and programs, debugging data, and upgrades.According to some embodiments, the external device 12 may also becapable of operating in two modes: a user mode that provides usefulclinical information to the patient or a caregiver, and a diagnosticmode that provides information to an individual for calibrating and/orservicing the external device 12 or for changing one or more parametersof the remote IMD 16 and/or pulse generator 14.

FIG. 4 is a flow chart showing an illustrative method 102 of adapting anacoustic link with an implantable medical device. The method 102 maycomprise, for example, a method of adapting an acoustic communicationlink between an external device 12 and a remote IMD 16, oralternatively, between a pulse generator 14 and a remote IMD 16. Themethod 102 may also be used to adapt an acoustic communication linkbetween the remote IMD 16 and another device implanted within the body.

The method 102 may begin generally with the step of establishing anacoustic link between the remote IMD 16 and another communicating devicesuch as the external device 12 and/or the pulse generator 14. Toinitiate the acoustic link, the external device 12 or pulse generator 14transmits an acoustic signal to the remote IMD 16 (block 104). Uponreceiving the acoustic signal, the remote IMD 16 enters into atransmission mode of operation and transmits an acoustic signal back tothe external device 12 or pulse generator 14 (block 106) that can thenbe used to measure the performance of the acoustic link between the twocommunicating devices (block 108). If, for example, the remote IMD 16receives an acoustic signal from the external device 12, the IMD 16transmits an acoustic signal back to the external device 12 that can beused by the external device 12 to measure the performance of theacoustic link between the remote IMD 16 and the external device 12.

In certain embodiments, the performance of the individual acoustic pathswithin one or more acoustic links can also be measured. For example, theperformance measuring step (block 108) can include measuring theperformance of an acoustic link established when the external device 12is the receiver and the remote IMD 16 is the transmitter. In addition,the external device 12 may individually measure the acoustic linkperformance when the external device 12 is the transmitter and theremote IMD 16 is the receiver. Any performance of other communicationpath(s) between the external device 12, the remote IMD 16, and/or one ormore additional IMDs may also be measured.

The performance of the acoustic link can be measured in a number ofdifferent ways. In certain embodiments, for example, the performance ofthe acoustic link can be measured by determining the number ofcommunication errors or timeouts that occur over a period of time, andthen comparing that number against a predetermined threshold stored in alook-up table. The performance of the acoustic link can also bedetermined by measuring the intensity of the acoustic signal and thencomparing the measured intensity level against a predetermined thresholdintensity level. Other means for measuring the performance of theacoustic link are also possible. For example, the performance of theacoustic link can be determined by reducing the transmitter power of theremote IMD 16, increasing the receiver threshold of the external device12 and/or pulse generator 16, and/or by varying the clock frequency.

Based on the measured performance of the acoustic link (block 108), theexternal device 12 next determines whether the acoustic link establishedbetween the two communicating devices is adequate based on the currentoperating parameters (block 110). The determination of whether theacoustic link is adequate can be accomplished, for example, using thecontroller 82 for the external device 12. Alternatively, and in otherembodiments, the determination of whether the acoustic link is adequatecan be accomplished by the controller 68 for the remote IMD 16. In someembodiments, both of the controllers 68,82 can be configured to assessthe performance of the acoustic link.

If at block 110 the performance of the acoustic link is adequate, theremote IMD 16 and external device 12 continue to operate using theircurrent operating parameters. Otherwise, if at block 110 the performanceof the acoustic link is inadequate, the external device 12 may adjustone or more operating parameters of the remote IMD 16 and/or theexternal device 12 in order to improve the link performance (block 112).Example operating parameters that can be adjusted to improve linkperformance can include, but are not limited to, increasing thetransmission power or intensity of the acoustic signal transmitted bythe remote IMD 16, increasing the receiving sensitivity or thresholds ofthe acoustic transducer 42 for the external device 12, adjusting thetransmission frequency of the acoustic signal transmitted by the remoteIMD 16, increasing the bit or word timing of the acoustic signaltransmitted by the remote IMD 16, increasing the sampling rate or wordsize of the acoustic signal transmitted by the remote IMD 16, and/orchanging the duty cycle of the bits transmitted by the remote IMD 16.

Once one or more operating parameters associated with the acoustic linkare adjusted (block 112), the external device 12 and/or remote IMD 16may then measure the performance of the acoustic link using the adjustedoperating parameter(s) (block 114). For example, if the power orintensity of the acoustic signal transmitted by the remote IMD 16 isincreased, the external device 12 may ascertain whether the performanceof the acoustic link improved over the previous power or intensitysetting (block 116). If at block 116 the performance of the acousticlink improves using the previous, adjusted operating parameter, theexternal device 12 and/or remote IMD 16 may repeat the process ofadjusting the operating parameter (block 112) (e.g., by a step function)and then measuring the performance of the acoustic link (block 114) inresponse to that adjusted operating parameter. The process of adjustingthe operating parameters may be repeated one or more times until, atblock 116, the adjusted operating parameter does not improve theperformance of the acoustic link. If, for example, an adjustment in thepower or intensity of the acoustic signal does not result in animprovement in the performance of the acoustic link, the remote IMD 16may then set the current power or intensity setting to the priorsetting. The method 102 may then be repeated one or more times, eitherautomatically by the remote IMD 16 and/or the communicating device12,14, or manually via a request from a user or process.

FIG. 5 is a flow chart showing another illustrative method 120 ofadapting an acoustic link with an implantable medical device. Method 120is similar to the method 102 of FIG. 4, but further includes the step(block 122) of operating the remote IMD 16 in a fail-safe mode ofoperation in the event the performance of the acoustic link is notimproved upon a change in the previous operating setting, and when theprior operating setting was inadequate to maintain the link performance.In some embodiments, for example, the fail-safe mode can be initiated ifno other adjustment in operating parameter was successful in restoringthe acoustic link to an acceptable performance level. In the fail-safemode, the remote IMD 16 may sacrifice certain performance criteria suchas speed or power usage to assure that an acceptable level ofperformance or other criteria (e.g., reliability, availability, etc.) ismaintained.

In some embodiments, the fail-safe mode may include an auto-transmitmode to improve the performance of the communication link. In certainembodiments, for example, the auto-transmit mode can be initiated withinthe remote IMD 16 if the external device 12 receives ten commands in arow from the remote IMD 16 and/or the pulse generator 14 withcommunication errors. When this occurs, the remote IMD 16 may initiatethe auto-transmit mode and transmit a data package having a fixed timingpattern such that the communicating device 12,14 can determine theremote IMD's 16 oscillator rate and adjust its oscillator rateaccordingly. The remote IMD 16 can also be configured to transmit otherparameters as part of the data package, including the pulse width andamplitude of the acoustic signal.

FIG. 6 is a flow chart showing another illustrative method 124 ofadapting an acoustic communication link with an implantable medicaldevice. As shown in FIG. 6, the method 124 may be initiated in responseto a request by a user (block 126). In some embodiments, for example,the link adjustment may be initiated manually by a caregiver or patiententering a command into an interface device (e.g., the user feedbackdevice 84) in response to an alarm or warning indicating that an errorin the communications has occurred. Alternatively, and in otherembodiments, the link adjustment may be initiated automatically by theremote IMD 16, or by a signal from a communicating device 12,14, toresolve any problems in the link availability, power efficiency, and/ordata reliability. In certain embodiments, for example, the method 124may be initiated automatically when the performance of the acoustic linkdrops below a predetermined threshold level.

Once initiated, the remote IMD 16 can be configured to set one or moreoperating parameters at an initial value, and then stepwise increaseeach operating parameter in order to improve the performance of theacoustic link between the remote IMD 16 and the communicating device. Inthe embodiment of FIG. 6, for example, the remote IMD 16 may initiallyset the transmission power of the acoustic signal provided by acoustictransducer 46 to a minimum level (block 128). Using this minimumtransmission power, the performance of the acoustic transmission is thenmeasured (block 130) at this minimum level. The transmission power isthen increased to a higher level (block 132), and the performance of theacoustic transmission is again measured at the new transmission level todetermine whether the increase in transmission power improves the linkperformance (block 134). If at decision block 136 the performance of thelink improves, the remote IMD 16 increases the power transmission levelto a higher level (block 132) and again measures the link performance(block 134) at this new value to determine whether the link performancefurther improves. The process of increasing the transmit power andmeasuring the link performance at each increase can be repeated one ormore times until, at such point, the link performance does not improve,or until a maximum transmission threshold value programmed within theremote IMD 16 is achieved. At this point, the remote IMD 16 may then setthe transmission power to the last setting that resulted in an increasein the link performance (block 138).

One or more other operating parameters may be adjusted in a similarmanner in order to further improve the performance of the acoustic linkbetween the remote IMD 16 and the external device 12 and/or pulsegenerator 14. In some embodiments, for example, the external device 12can be configured to initially set the receiving acoustic transducer toa minimum sensitivity or threshold (block 140). Using this minimumreceiver sensitivity or threshold, the external device 12 then measuresthe performance of the acoustic transmission at this minimum level(block 142). The receiver sensitivity is increased and/or the thresholddecreased (block 144), and the performance of the acoustic link is againmeasured to determine whether the performance has improved (block 146).If at decision block 148 the performance of the link improves, theexternal device 12 may repeat the process of increasing the sensitivityor threshold level (block 144) and measuring the link performance (block146) at this new sensitivity or threshold level to determine whether thelink performance further improves. The process may then be repeated oneor more times until, at such point, the link performance does notimprove, or a maximum sensitivity or threshold value is achieved. Theexternal device 12 may then set the receiver sensitivity or thresholdvalue to the previous setting that resulted in an increase in the linkperformance (block 150).

The carrier frequency used to modulate the acoustic signal transmittedby the remote IMD 16 can be further adjusted to increase the performanceof the acoustic link. In some embodiments, for example, the carrierfrequency for the remote IMD 16 can be initially set to a minimumfrequency (block 152). Using this minimum carrier frequency, theexternal device 12 then measures the performance of the acoustictransmission at this minimum level (block 154). The carrier frequency isthen increased to a higher frequency (block 156), and the performance ofthe acoustic link is again measured at the increased frequency todetermine whether the link performance improved (block 158). If atdecision block 160 the performance of the link improves, the process ofincreasing the carrier frequency (block 156) and measuring the linkperformance (block 158) at the new carrier frequency is repeated.Otherwise, if the performance does not improve, the remote IMD 16 mayset the carrier frequency to the last frequency that resulted in anincrease in the link performance (block 162).

The bit timing of the acoustic signal, representing the timing betweensuccessive bits or words in the acoustic signal, can be further adjustedto increase the performance of the acoustic link. The bit timing mayrepresent, for example, factors such as the data rate, pulse width, andthe bit or word interval of the data stream transmitted as part of theacoustic signal. The remote IMD 16 initially sets the bit timing to aminimum value (block 164), which is then analyzed by the external device12 and/or pulse generator 14 in order to measure the performance of theacoustic transmission using the minimum bit timing (block 166). The bittiming is then increased to a higher rate (block 168), and theperformance of the acoustic link is again measured at the increased bitrate to determine whether the link performance improved (block 170). Ifat decision block 172 the performance of the link improves, the processof increasing the bit timing (block 168) and measuring the linkperformance (170) at the new bit timing value is repeated. Otherwise, ifthe performance does not improve, the remote IMD 16 may set the bittiming value to the last value that resulted in an increase in the linkperformance (block 174).

The sampling rate or word resolution can be further adjusted to increasethe performance of the acoustic link. The remote IMD 16 initially setsthe sampling rate or word resolution to a minimum value (block 176).Using this minimum value, the external device 12 then measures theperformance of the acoustic link at this minimum level (block 178). Thesampling rate or word resolution is then increased to a higher rate orresolution (block 180), and the performance of the acoustic link isagain measured at the increased rate or resolution to determine whetherthe link performance improves (block 182). If at decision block 184 theperformance of the link improves, the process of increasing the samplingrate or word resolution (block 180) and measuring the link performance(block 182) at the new rate or resolution is repeated. Otherwise, if theperformance does not improve, the remote IMD 16 may set the samplingrate or word resolution to the previous value that resulted in anincrease in the link performance (block 186). As indicated generally atblock 188, once one or more of operating parameters associated with theacoustic link have been adjusted, the remote IMD 16 may then terminatethe algorithm and await another user request (block 126) to initiate themethod 124.

The ordering of the operating parameters that are adjusted may differfrom that shown in the illustrative method 124 of FIG. 6. In someembodiments, only operating parameters associated with the transmissionof the acoustic signal by the remote IMD 16 are adjusted to improve theperformance of the acoustic link. In other embodiments, only operatingparameters associated with the reception of the acoustic signal by theexternal device 12 and/or pulse generator 14 are adjusted to improve thelink performance.

In addition, although FIG. 6 depicts several illustrative operatingparameters that can be adjusted in order to improve link performance, inother embodiments other types of operating parameters can also beadjusted in a similar fashion. In some embodiments, for example, themodulation format (e.g., PCM, FSK, FM, AM, etc.) of the acoustic signaltransmitted by the remote IMD 16 can be adjusted in order to improvelink performance. In one such embodiment, for example, the remote IMD 16may switch from one modulation format (e.g., FSK) to a second, differentmodulation format (e.g., FM) in order to increase the bandwidth of theacoustic signal. The remote IMD 16 can also be configured to adjust thetype of error correction employed to detect communications errors,including type-based error checking and correction (e.g., parity, cyclicredundancy check (CRC), etc.) and interval-based error checking andcorrection (e.g., bit, word, block, etc.). For example, the remote IMD16 can be configured to switch from a relatively low-level errorchecking technique (e.g., parity error detection) to a relativelyhigh-level error checking technique (e.g., CRC) in the event greatererror checking and correction is required to maintain the acoustic link.

In certain embodiments, the antenna gain or directionality of theacoustic transmission can be adjusted in order to improve theperformance of the acoustic link. In one such embodiment, the acoustictransducer 42 for the external device 12 and/or the acoustic transducer46 for the remote IMD 16 may include a phased-array of ultrasonictransducer elements. To improve the directionality of the acoustictransmission, phase delay adjustments can be provided on one or more ofthe ultrasonic elements within the array in order to manipulate theacoustic transmission through the body. By adjusting the directionalityof the acoustic transmission, a greater portion of the acoustic signalcan be received by the external device 12 and/or the pulse generator 14,thus increasing the performance of the acoustic link.

The transmission frequency of the acoustic signal can also be adjustedin order to improve the performance of the acoustic link. In one suchembodiment, the frequency of the transmitted acoustic signal can beadjusted by sweeping the frequency of the acoustic signal across a rangeof frequencies, and at each frequency or at multiple, discretefrequencies, measuring the power or intensity of the acoustic signal.The operation frequency can then be set at a frequency that produces theacoustic signal with the greatest power or intensity.

In certain embodiments, the method 124 can be configured to adjust oneor more operating parameters of the remote IMD 16 in order to maintain aminimally acceptable performance of the acoustic link. If, for example,the current operating parameter is determined by the controller 68 to besufficient to establish an adequate acoustic communication link betweenthe remote IMD 16 and the receiver, the method 124 may continue tooperate using the current parameter until, at such point, furtheradjustment to the parameter is necessary to maintain the acoustic link.With respect to the step of measuring the link performance (block 134)in response to the current transmit power setting, for example, thecontroller 68 may conclude that the current transmit power setting issufficient to maintain a minimal level of performance, and thus continueoperation using this setting until the performance of the acoustic linkfalls below a threshold value. Maintaining the operating parameter atthis minimum threshold level may be useful, for example, for limitingthe amount of acoustic exposure the patient receives while stillmaintaining an adequate link with the receiver. Maintaining theoperating parameter at this minimum threshold may also be used toconserve power consumption from the energy storage device 56 as well ascomputational resources from the controller 68.

Various modifications and additions can be made to the exemplaryembodiments discussed without departing from the scope of the presentinvention. For example, while the embodiments described above refer toparticular features, the scope of this invention also includesembodiments having different combinations of features and embodimentsthat do not include all of the described features. Accordingly, thescope of the present invention is intended to embrace all suchalternatives, modifications, and variations as fall within the scope ofthe claims, together with all equivalents thereof.

What is claimed is:
 1. A method of adapting the performance of anacoustic communication link between an implantable medical device and acommunicating device, the method comprising: initiating an acoustic linkwith the implantable medical device; measuring an initial performance ofthe acoustic link; determining whether the initial performance of theacoustic link is adequate by comparing a performance parameter of theacoustic link against a redetermined threshold performance parameterstored within a controller; and adjusting at least one operatingparameter related to the acoustic link in the event the initialperformance of the acoustic link is inadequate, the at least oneoperating parameter including a parameter related to at least one of thetransmission or reception of an acoustic signal via an acoustictransducer.
 2. The method of claim 1, further comprising: measuring aperformance of the acoustic link in response to the at least oneadjusted operating parameter; and setting the at least one operatingparameter to a prior setting if the measured performance of the acousticlink does not improve in response to the at least one adjusted operatingparameter.
 3. The method of claim 1, wherein establishing an acousticlink with the implantable medical device includes transmitting a wake upsignal from the communicating device to the implantable medical device,the wake up signal adapted to actuate the implantable medical devicefrom a sleep state to an active state.
 4. The method of claim 1, whereinthe communicating device is an external device.
 5. The method of claim1, wherein the communicating device is an implantable device.
 6. Themethod of claim 1, wherein the performance parameter includes a signalstrength of an acoustic signal received by the communicating device. 7.The method of claim 1, further including operating the implantablemedical device in a fail-safe mode of operation in the event theperformance of the acoustic link is not improved upon a change in theadjusted operating parameter.
 8. The method of claim 7, wherein, in thefail-safe mode of operation, the implantable medical device is adaptedto transmit a data package at a fixed timing pattern to thecommunicating device.
 9. The method of claim 1, wherein adjusting atleast one operating parameter related to the acoustic link and measuringa performance of the acoustic link in response to the at least oneadjusted operating parameter is repeated one or more times until theperformance of the acoustic link in response to the adjusted operatingparameter does not improve.
 10. The method of claim 1, wherein the atleast one operating parameter includes at least one of a transmissionpower parameter, a receiver sensitivity or threshold level parameter, acarrier frequency parameter, a bit timing parameter, a sampling rate orword size parameter, a transmission frequency parameter, an antenna gainor directionality parameter, a modulation format parameter, and an errorchecking or correction parameter.
 11. The method of claim 1, wherein theat least one operating parameter further includes an operating parameterassociated with an acoustic signal received by the communicating device.12. The method of claim 1, wherein implantable medical device includes aphysiological sensor adapted to sense at least one physiologicalparameter within the body.
 13. A method of adapting the performance ofan acoustic communication link between an implantable medical device anda communicating device, the method comprising: initiating an acousticlink between the implantable medical device and one or morecommunicating devices, each communicating device including at least oneacoustic transducer adapted to transmit or receive acoustic signals, anda controller adapted to measure at least one parameter associated withthe performance of the acoustic link; measuring a performance of theacoustic link; comparing a performance parameter of the acoustic linkagainst a predetermined threshold performance value stored within thecontroller; and adjusting at least one operating parameter related tothe acoustic link in the event the performance of the acoustic link isinadequate, the at least one operating parameter including a parameterrelated to the transmission of an acoustic signal from the acoustictransducer of the implantable medical device.
 14. A system, comprising:an implantable medical device including a physiological sensor and anacoustic transducer adapted to transmit and receive acoustic signals; acommunicating device in acoustic communication with the implantablemedical device via an acoustic link, the communicating device includingan acoustic transducer adapted to transmit and receive acoustic signals;and a means for measuring a performance parameter of the acoustic link,comparing the measured performance parameter against a predeterminedthreshold performance parameter stored within a controller of theimplantable medical device or communicating device, and adjusting atleast one operating parameter of the implantable medical device or thecommunicating device in response to a measured performance parameter.15. The system of claim 14, wherein the communicating device is anexternal device.
 16. The system of claim 14, wherein the communicatingdevice is an implantable device.
 17. The system of claim 16, wherein theimplantable device is a pulse generator.
 18. The system of claim 14,wherein said means includes a processor adapted to adjust at least oneoperating parameter of the implantable medical device in response to ameasured performance of the acoustic link.
 19. The system of claim 14,wherein said means includes a processor adapted to adjust at least oneoperating parameter of the communicating device in response to ameasured performance of the acoustic link.